DESCRIPTION: A fundamental issue in muscle physiology is the regulation of oxygen transport to the mitochondria, since oxygen consumption can vary over a wide range, depending upon stimulation or exercise condition. Yet measuring vascular and intracellular oxygen has been extremely elusive. For vascular p02, investigators have recently noted that the water signal in leg muscle shifts with ischemia. The observation implies that the source of the shift may originate from Hb deoxygenation. If so, that paramagnetic transition during Hb deoxygenation can enhance the T2*, as functional magnetic resonance imaging studies have demonstrated, but also can shift the water line. The effect arises from the bulk magnetic susceptibility and the given limb geometry relative to main magnetic field. Consequently a calibrated curve of the water shift could then reflect the vascular p02. The project will specifically aim to determine the relationship between the chemical shift of water as a function of Mb and Hb oxidation states in analytical solutions and to establish the theoretical basis for utilizing the magnetic susceptibility induced H20 chemical shift as a p02 indicator. The results would open a new approach to measuring vascular p02 in muscle in other tissues.